Central heating pump sizing

[John.g]

I can certainly suggest a 6m Wilo Yonos Pico that I installed 2 years ago in my 10 rad system like your own and it works perfectly, Grundfos or DAB is often the preferred choice of some, I will suggest one later.

Because you have chemically cleaned you system regularly, I would install the pump first and see how your system performs, if performing exactly the same, I would immediately remove it and re install the old pump until the power wash or whatever is carried out.
But if you are handy yourself, it only takes less than a hour to remove the existing pump head, inspect. clean and replace, the impeller may just be full of crap.

The pump head is the differential pressure (head) measured in meters between the pump suction and discharge and the chosen pump differential head required depends on the frictional resistances in the systems piping, radiator & fittings, boiler Hx resistance etc. at the required flow rate. A 6M pump will be quite adequate for most domestic systems but its very rarely that the pump would have to run on speed3 as a much lower head of say 2.5 to 3.5M is only needed to give the required flow rate.

 

[SJB060685]

If we had an idea of extension and existing pipework sizes and runs we could guesstimate a bit further.
Furthermore I just want to thank you again John. I've never really dived into the exacts of pump characteristics, partly because I've never needed to and partly because of laziness maybe but my understanding now is better.

 

[Reddwarf4ever]

I can certainly suggest a 6m Wilo Yonos Pico that I installed 2 years ago in my 10 rad system like your own and it works perfectly, Grundfos or DAB is often the preferred choice of some, I will suggest one later.

Because you have chemically cleaned you system regularly, I would install the pump first and see how your system performs, if performing exactly the same, I would immediately remove it and re install the old pump until the power wash or whatever is carried out.
But if you are handy yourself, it only takes less than a hour to remove the existing pump head, inspect. clean and replace, the impeller may just be full of crap.

The pump head is the differential pressure (head) measured in meters between the pump suction and discharge and the chosen pump differential head required depends on the frictional resistances in the systems piping, radiator & fittings, boiler Hx resistance etc. at the required flow rate. A 6M pump will be quite adequate for most domestic systems but its very rarely that the pump would have to run on speed3 as a much lower head of say 2.5 to 3.5M is only needed to give the required flow rate.

I can certainly remove the pump for cleaning. The Pico you have is 6m, does that mean 6m head ? So when you refer to a pump size by head, is this a different way of saying differential pressure ?
I will check the pump first and if clean, will replace with one as suggested..the restriction is as. See it...1 - the pump 2 - sludge build up in the pipework and or HX 3 - pipework modifications
FYI the extension added 6 extra rooms and a 30% increase to the lounge......

looking forward to seeing suggestions of pumps, Amazon links would help, pump numbering could be an issue in searching

is this the one you have ? https://smile.amazon.co.uk/Wilo-421...ords=6m+Wilo+Yonos+Pico&qid=1609116976&sr=8-3

whats the numbering mean ? There are so many similar models are greatly different prices

 

[John.g]

Yes, that's my pump, 6M or whatever always refers to the differential pressure head.

Referring to these numbers.

Wilo 4215516 YONOS PICO 25/1-6-130-(Row), Green​

the 4215516 is probably the Wilo model number.
25 is the diameter of the pump ports in MM.
1-6 is the operating range in meters.
130 is the distance in MM between the pump end connections and is very important as some pumps are "longer" so measure this on your own pump, if not 130mm then you will have to crop and remake one compression fitting which would mean system drain down.
Don't know what ROW means.

Am I correct in assuming that your house with extension has 10 rads?.

Here is a link to a DAB Evosta 3 which is a 7M pump (which you may prefer) which displays power, flow rate and pump head, just make sure before purchase that you are getting this exact model with that display. It also seems exceptional value for money and I would have no hesitation in recommending it.

https://www.stuartplumbing.co.uk/dab-evosta-circulating-central-heating-pump-replacement-grundfos-pump/

 

[SJB060685]

6 extra rooms and a 30% increase to the longe will add quite a lot of resistance to the circuit, on top of what was already there.

 

[Reddwarf4ever]

Yes, that's my pump, 6M or whatever always refers to the differential pressure head.

Referring to these numbers.

Wilo 4215516 YONOS PICO 25/1-6-130-(Row), Green​

the 4215516 is probably the Wilo model number.
25 is the diameter of the pump ports in MM.
1-6 is the operating range in meters.
130 is the distance in MM between the pump end connections and is very important as some pumps are "longer" so measure this on your own pump, if not 130mm then you will have to crop and remake one compression fitting which would mean system drain down.
Don't know what ROW means.

Am I correct in assuming that your house with extension has 10 rads?.

Here is a link to a DAB Evosta 3 which is a 7M pump (which you may prefer) which displays power, flow rate and pump head, just make sure before purchase that you are getting this exact model with that display. It also seems exceptional value for money and I would have no hesitation in recommending it.

https://www.stuartplumbing.co.uk/dab-evosta-circulating-central-heating-pump-replacement-grundfos-pump/

Thanks for the numbering info, mine is a 130mm a Wilo Gold, the link you gave shows a 5m pump, However the specs say up to 6.9m, bit confusing unless incorrectly listed....also

MPN	60161174 doesn’t mention the on pump displays you mention, unless it’s a different model ?

Certainly sounds good, DAB also come with a 3 year guarantee.

P.S. I have 12 radiators includes 3 towel rads

 

[John.g]

The Wilo is a 6M pump (your link). The DAB (my link) is a 7M (6.9) pump.

• "Operating range: from 0.4 to 3.3 m3/h with head up to 6.9 meters."

Don't have any code but the description should be enough ie DAB Evosta 3 but check with your supplier.

 

[Reddwarf4ever]

The Wilo is a 6M pump (your link). The DAB (my link) is a 7M (6.9) pump.

• "Operating range: from 0.4 to 3.3 m3/h with head up to 6.9 meters."

Don't have any code but the description should be enough ie DAB Evosta 3 but check with your supplier.

Hi
the link you gave shows a 5m pump but specs say 6.9m also no mention of the display options, have emailed them and also DAB evosta, their email address is not on their website, but on the very last page of the downloadable [email protected]
sounds very promising, as you say, need to get the right one.....Amazon have loads of V3 various prices....

the DAB pump has 40 as the connection size, my Wilo Gold is 25mm will that be an issue ?

 

[John.g]

The "normal" connection size is 1.25 ins which is the internal dia of the threaded part, I measured the OD of the threaded part at ~ 47.6mm, measurement across the flats on the isol valve(s) attaching nuts is 2 ins. (51 mm)

 

[Reddwarf4ever]

The "normal" connection size is 1.25 ins which is the internal dia of the threaded part, I measured the OD of the threaded part at ~ 47.6mm, measurement across the flats on the isol valve(s) attaching nuts is 2 ins. (51 mm)

Wilo 4215516 YONOS PICO 25/1-6-130-(Row), Green​

the 4215516 is probably the Wilo model number.
25 is the diameter of the pump ports in MM.
My Wilo Gold is also quoted as 25, just confused why the DAB has a 40 at the beginning of the number ???

The Wilo is a 6M pump (your link). The DAB (my link) is a 7M (6.9) pump.

• "Operating range: from 0.4 to 3.3 m3/h with head up to 6.9 meters."

Don't have any code but the description should be enough ie DAB Evosta 3 but check with your supplier.

 

[Reddwarf4ever]

6 extra rooms and a 30% increase to the longe will add quite a lot of resistance to the circuit, on top of what was already there.

That’s what I was afraid of....tried this morning with the Hot water on also, at first it looked like like the flow was better ( maybe it should be with such a short circuit, maybe equiv to a CH bypass ) but although initially it needed 10KW and had a DT of 27oC it settled down to the usual 7-8KW DT of 21-22oC with a target temperature of 72oC, so not much difference.....I hope getting a 7m head pump will help improve the flow

 

[John.g]

7.5kw heating demand at a deltaT of 21C = a flowrate of 5.1 LPM which requires a 5.1M head assuming a healthy pump. You require a flowrate of ~ 15 LPM which theoretically requires a head of (15/5.1)^2 X 5.1 or 44M so hope you have a very unhealthy pump just now.

 

[Reddwarf4ever]

7.5kw heating demand at a deltaT of 21C = a flowrate of 5.1 LPM which requires a 5.1M head assuming a healthy pump. You require a flowrate of ~ 15 LPM which theoretically requires a head of (15/5.1)^2 X 5.1 or 44M so hope you have a very unhealthy pump just now.

I read this several times but even though I have worked as a refinery process operator for 20 years & have C&G in process control, I just can’t understand this.....sorry

 

[Reddwarf4ever]

Yes, that's my pump, 6M or whatever always refers to the differential pressure head.

Referring to these numbers.

Wilo 4215516 YONOS PICO 25/1-6-130-(Row), Green​

the 4215516 is probably the Wilo model number.
25 is the diameter of the pump ports in MM.
1-6 is the operating range in meters.
130 is the distance in MM between the pump end connections and is very important as some pumps are "longer" so measure this on your own pump, if not 130mm then you will have to crop and remake one compression fitting which would mean system drain down.
Don't know what ROW means.

Am I correct in assuming that your house with extension has 10 rads?.

Here is a link to a DAB Evosta 3 which is a 7M pump (which you may prefer) which displays power, flow rate and pump head, just make sure before purchase that you are getting this exact model with that display. It also seems exceptional value for money and I would have no hesitation in recommending it.

https://www.stuartplumbing.co.uk/dab-evosta-circulating-central-heating-pump-replacement-grundfos-pump/

Found it cheaper https://plumbingsuppliesdirect.co.uk/dab-evosta-replacement-grundfos-circulating-heating-pump/
just need to confirm it’s a straight swop for my Wilo Gold, will phone them tomorrow

 

[John.g]

I read this several times but even though I have worked as a refinery process operator for 20 years & have C&G in process control, I just can’t understand this.***.sorry

OK, you have determined that you had/have a heating demand of ~ 7.5kw with a deltaT of 21C. By calculation, the flowrate is, 7.5*860/21/60, or 5.1 LPM. Go to the pump curves and you will see that the punp will give this flow at a head of 5.1/5.2M. Now you either have a big restriction somewhere or a very unhealthy pump because if the pump is OK then to increase that flowrate to 15 LPM will need a differential head of 44M, flow is prop to the sqroot of head and head is prop to flow squared. so required head is 5.1X (15/5.1)^2, 44M.

 

[SJB060685]

John do you mind sharing how you calculate flow is proportion to square root of head? I think I'm doing it wrong

 

[Reddwarf4ever]

OK, you have determined that you had/have a heating demand of ~ 7.5kw with a deltaT of 21C. By calculation, the flowrate is, 7.5*860/21/60, or 5.1 LPM. Go to the pump curves and you will see that the punp will give this flow at a head of 5.1/5.2M. Now you either have a big restriction somewhere or a very unhealthy pump because if the pump is OK then to increase that flowrate to 15 LPM will need a differential head of 44M, flow is prop to the sqroot of head and head is prop to flow squared. so required head is 5.1X (15/5.1)^2, 44M.

Thanks, seems cleaner now, obviously it would be impossible to give my pump a 44m head....the DAB pump you linked to looks perfect, found an even cheaper site £62.39 inc and free postage......but is this interchangeable for my Wilo gold.....the first numbers are different, don’t I need a 25mm pump ?
one other thought, just before the expansion pipe was joined to the F&E inlet I was experiencing occasional hot water venting into the F&E tank, if this still continues, but now goes into the inlet, could this be causing the inefficiency ? Maybe I can check where it’s joined and se if it’s hot thanks

 

[John.g]

John do you mind sharing how you calculate flow is proportion to square root of head? I think I'm doing it wrong

I have never calculated it but this chap Bernoulli has and it seems to be reasonably accurate.

 

[SJB060685]

I have read on him yes. Im just running numbers and trying to figure out the resulting flow from the square root of head. Clearly im not doing something right

 

[John.g]

Thanks, seems cleaner now, obviously it would be impossible to give my pump a 44m head....the DAB pump you linked to looks perfect, found an even cheaper site £62.39 inc and free postage...but is this interchangeable for my Wilo gold..the first numbers are different, don’t I need a 25mm pump ?
one other thought, just before the expansion pipe was joined to the F&E inlet I was experiencing occasional hot water venting into the F&E tank, if this still continues, but now goes into the inlet, could this be causing the inefficiency ? Maybe I can check where it’s joined and se if it’s hot thanks

I think the 25 or 15 refers to the pump ports internal diameter so shouldn't affect any of the other dimensions.

No, don't think any problem now as the reason for joining the cold feed and vent was/is to destroy the effect of any imbalances in a U tube.

 

[John.g]

I have read on him yes. Im just running numbers and trying to figure out the resulting flow from the square root of head. Clearly im not doing something right

You mean mathematically?. if a differential head of 3M results in a flow of say 13 LPM (like my heating system) and I increase the (pump) head to say 5M, the resultant flow will be the original Flow X the sqroot of the (newhead/oldhead).....13X sqroot(5/3) = 13X1.29 = 16.77 LPM.

 

[SJB060685]

You mean mathematically?. if a differential head of 3M results in a flow of say 13 LPM (like my heating system) and I increase the (pump) head to say 5M, the resultant flow will be the original Flow X the sqroot of the (newhead/oldhead)***..13X sqroot(5/3) = 13X1.29 = 16.77 LPM.

Thanks buddy. That makes sense now

 

[Reddwarf4ever]

You mean mathematically?. if a differential head of 3M results in a flow of say 13 LPM (like my heating system) and I increase the (pump) head to say 5M, the resultant flow will be the original Flow X the sqroot of the (newhead/oldhead)***..13X sqroot(5/3) = 13X1.29 = 16.77 LPM.

Although they both have this part number DAB 60161174, the images look different......the Amazon one is more expensive Andries than even look like it has the data display.....
Will phone PSD tomorrow and confirm, think this is my best hope, seems a very good price £62.39 inc free postage....any thoughts ? 1st image PSD 2nd image Amazon

 

[John.g]

Every time one looks at these pumps they seem to change spec/display, Grundfos is the same, they must be breeding them, just ensure you are getting the one with the proper display.

 

[Reddwarf4ever]

Every time one looks at these pumps they seem to change spec/display, Grundfos is the same, they must be breeding them, just ensure you are getting the one with the proper display.

That’s the one on the left, curious how prices vary, £60-£150.....eBayera are an optimistic breed

 

[Reddwarf4ever]

Every time one looks at these pumps they seem to change spec/display, Grundfos is the same, they must be breeding them, just ensure you are getting the one with the proper display.

Problem is, I have just been advised this is a 180mm length pump whereas mine is 130mm, is that correct ?

 

[John.g]

A bit surprised at that, don,t know dimensions of your own one, the wilo gives practically the same output, will check in morning to compare and advise, measure your own to confirm 130mm

 

[John.g]

A bit surprised at that, don,t know dimensions of your own one, the wilo gives practically the same output, will check in morning to compare and advise, measure your own to confirm 130mm

The DAB3 appears to be a 8M pump hence the 180mm between centers so I would advise against this as it involves piping mods and drain down, also 130mm centers gives you more choice of 6/7M pumps.

While the Wilo or Dab Evosta2 (no display) will almost certainly give you the required head/flow I think you are better off installing a pump like a Grundfos UPS3 15-50/65 which is very powerful 6.5M pump which will satisfy your needs with ease. For example it will pump 33LPM @ 4.5M, Dab2, 33LPM @ 3M and the Wilo 33LPM @ 3.2m.

Unfortunately, this UPS3 does not display watts but not the end of the world as you really only need this as an aid to see if you have a pump problem or a restriction. By spending a few extra bob you can buy a nice little plug in energy monitor, I have a few and they are quite accurate, (see link) and use it like this.

I assume you intend to clean the existing pump head so before removal/clean, remove the pump lead and fit a 3 pin plug. ensure boiler off and any zone valves if fitted, latched open, plug in the pump lead to the energy monitor in turn plugged in to any convenient socket or extension lead, note the watts, remove plug, clean pump head and ports, then re measure power.
Depending on findings, if you do decide to install the UPS3 or whatever, do likewise, stick a 3 pin plug on it and you can then monitor its power in its different operating modes and then run the pump on the appropriate setting. When tests complete re install pump lead to wiring center.

One word of caution if removing the pump by opening the isol valve nuts, these can be extremely difficult to undo, I have change out a few pumps for neighbors and one of my own and have always drained down and removed the pump complete with isol valves, I then found it quite difficult to remove the pump valves even though I obviously renewed them with the new pump.

https://www.amazon.co.uk/Monitor-Electricity-Display-Consumption-Analyzer/dp/B08KZGM1P7/ref=asc_df_B08KZGM1P7/?tag=googshopuk-21&linkCode=df0&hvadid=463168730140&hvpos=&hvnetw=g&hvrand=3905167764382884732&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=1007835&hvtargid=pla-1020257457799&psc=1

PS: fairly sure your pump has 130mm centers but best to measure up.

 

[Reddwarf4ever]

Thanks for all the advice, sounds like the way to go.....will investigate the power to my pump, looks rather complicated, as this also had its wiring modified.....when an electrician came round a few years ago, he made some changes, involved lifting up the floor board to get access o the connections ( my dam extension buile
der ) found he had used a light switch as a junction box, now the new junction box in the immersion cupboard, but looks complex.....will have a careful look, taking photos as I go....all good fun what’s the LPM of the DAB3 ? Do like the idea of the displays, womder how it displays the flow, ant be a calculation as it doesn’t know the Delta T, must be an integral flow meter

I don’t suppose a replacement pump comes with new valves, assume would have to be bought separately my CH pump iso valves have no handles, never have, can these be bought separately ? Be so much easier to isolate

 

[John.g]

Your old pump isolating valves are probably 1/4 turn ball valves that you shut with a screwdriver (slot) or a allen key, nothing sticks out, but unfortunately they almost always leak after operation, you can easily buy new ones with gate valves.

It would seem that you can get a Dab Evosta3 with 130mm centres. it might be a 6.5/7M pump but you should ask your supplier if they have one, this will also be adequate IMO, the pump curves for all their models are in the link.

https://evosta.dabpumps.com/wp-content/uploads/2019/03/Evosta-2-3-Installation-and-Operation-Manual_UK.pdf

 

[Reddwarf4ever]

Your old pump isolating valves are probably 1/4 turn ball valves that you shut with a screwdriver (slot) or a allen key, nothing sticks out, but unfortunately they almost always leak after operation, you can easily buy new ones with gate valves.

It would seem that you can get a Dab Evosta3 with 130mm centres. it might be a 6.5/7M pump but you should ask your supplier if they have one, this will also be adequate IMO, the pump curves for all their models are in the link.

https://evosta.dabpumps.com/wp-content/uploads/2019/03/Evosta-2-3-Installation-and-Operation-Manual_UK.pdf

have ordered the DAB 3 21412 model, not sure which curve is applicable to the pump I ordered.... some websites don’t give the numbering, just the performance data, the site I bought mine from had some contradictory info, confirmed it was 130mm and 6.9m head by phone and has a 5 year guarantee not 3 as shown, hopefully they will change the info on their site...ordered it from https://plumbingsuppliesdirect.co.uk/dab-evosta-replacement-grundfos-circulating-heating-pump/ but the invoice is from STUART PLUMBING & HEATING SUPPLIES, but on their website it’s more expensive and have to pay postage so assume PSD is owned by Stuart plumbing.....must be offering competition to their own company.....marketing strategy the pump seems to have numerous control options, what’s my best setting to start with ? And best setting long term....

P.S. the pump iso valves are gate valves, not quarter turn, with a single square 1/4” approx post, no thread that I can see to hold a handle, can’t understand why they are sold like this, to shut off in an emergency, requires hunting around for an adjustable ( or normal ) spanner.....so much easier with a handle......maybe will replace them when I change the pump

 

[SJB060685]

John what would happen to the watts display if there was a pump problem or restriction in the system?

 

[John.g]

have ordered the DAB 3 21412 model, not sure which curve is applicable to the pump I ordered.* some websites don’t give the numbering, just the performance data, the site I bought mine from had some contradictory info, confirmed it was 130mm and 6.9m head by phone and has a 5 year guarantee not 3 as shown, hopefully they will change the info on their site...ordered it from https://plumbingsuppliesdirect.co.uk/dab-evosta-replacement-grundfos-circulating-heating-pump/ but the invoice is from STUART PLUMBING & HEATING SUPPLIES, but on their website it’s more expensive and have to pay postage so assume PSD is owned by Stuart plumbing.*.must be offering competition to their own company..marketing strategy the pump seems to have numerous control options, what’s my best setting to start with ? And best setting long term.

P.S. the pump iso valves are gate valves, not quarter turn, with a single square 1/4” approx post, no thread that I can see to hold a handle, can’t understand why they are sold like this, to shut off in an emergency, requires hunting around for an adjustable ( or normal ) spanner..so much easier with a handle...maybe will replace them when I change the pump

You have the correct type isol valves as the gland nut can be tightened up if any leak, so no need for renewal.

Would suggest constant pressure, either CP2 or CP3 see below, answer to SJB.

 

[John.g]

John what would happen to the watts display if there was a pump problem or restriction in the system?

Look at the pump curve on pge 25 in attachment which is for a 7M Evosta2, can,t find one for a 7M evosta3.
you will see that on constant pressure CP3 that the pump will maintain 4.8M from 0 flow, if the system demand is 1 m3/hr 16.7 lpm then the pump power is 35w, if a restriction in the system and the flow fell to zero then the power is 16.5w and so on in between. more later

 

[SJB060685]

Look at the pump curve on pge 25 in attachment which is for a 7M Evosta2, can,t find one for a 7M evosta3.

Which chart am I looking at?
Through common sense I imagine if there was a restriction on PP then the pump would modulate down and display a lower wattage?